Kate Middleton, Prince Harry lead tributes for Queen Elizabeth ahead of milestone 90th birthday

Ahead of her 90th birthday on April 21, Queen Elizabeth has been praised by those closest to her for the "huge amount of joy" that she brings to people. In a documentary that aired on ITV on Sunday to celebrate the monarch's milestone birthday, the Duchess of Cambridge, Prince Harry,Princess Eugenie and the Countess of Wessex have all paid tribute to the long-standing royal.

Duchess Kate, 34, spoke out about Her Majesty’s relationship with people, saying: "I think she’s so, so engaging. I think she has got the most fantastic smile and I think if the Queen does nothing but smiles, it gives people a huge amount of joy and a huge amount of pleasure.

" She’s so dignified and calm…everyone feels that they've had some quality time with Her Majesty – and also a real personal connection, and I think that's a real skill."

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The Queen will turn 90 on April 21 Photo: Getty Images

The Duchess also showed her admiration for the Queen’s energy and devotion to duty, even as a young mother to Prince Charles,Princess Anne, Prince Andrew and Prince Edward. "I have no idea where she gets her energy from – I need to go and ask a few more questions," she said. "Being a mother and new in my job as well, I have no idea how the Queen has done it – with four children of her own."

Continuing, Prince George and Princess Charlotte's mom noted, "To manage all of those elements of your life – from the family, to the work as well as to the national importance of her role – it’s extraordinary. And for so long too – I think it’s really incredible."

Kate’s comments came in her first solo TV interview, which for Our Queen at Ninety. She also remarked on the monarch’s modest tastes, saying: "What’s really struck me is her love for the simple things in life. You would expect a lot of grandeur and a lot of fuss. Actually what really resonates with me is her love for simple things, the lack of fuss - and it’s a special quality to have."

The Duchess revealed how she and William admire the Queen’s closeness to her husband the Duke of Edinburgh, saying: "All the time William and I are so struck by the Queen's sense of duty and commitment. And I think to do that by yourself would be a very lonely place to be.

Kate and Harry both shared kind words about Her Majesty Photo: Getty Images

"But I think to have the support of your husband there by your side on those occasions – and behind closed doors as well – I think is really special." Laughing, she added: " William and I have got quite a long way to go. But, no, it really, really is fantastic. And to have seen and experienced as much as they have together, it's really special."

After revealing how Her Majesty always leaves out gifts for Prince George and Princess Charlotte when they go to stay with her, Kate described the Queen as "hugely thoughtful."

She said: "I can remember being at Sandringham for the first time at Christmas and I was worried what to give the Queen as her Christmas present. And I was thinking, ‘Gosh! What shall I give her?’

Princess Eugenie praised her grandmother's timeless style Photo: Getty Images

"And I thought back to perhaps what would I give my own grandparents. I thought I'll make her something, which could have gone horribly wrong. I decided to make some - actually it was my granny's recipe for chutney. And I was slightly worried about it.

"But I noticed the next day that it was on the table. And I think such a simple gesture went such a long way for me. I've noticed since that she's done that on lots of occasions and I think it just shows her thoughtfulness really - her care in looking after everybody."

Elsewhere in the documentary, Princess Eugenie praised her grandmother’s timeless fashion sense, saying: "Lots of my friends say, ‘Oh she's just the best style person there is, you know, she looks great in her clothes. The style is something that is very unique to her."

The 26-year-old described the Queen’s look as "elegant, classic," adding: " She's got a wonderful, happy color to her at all times. I think that's the word – happy."

The Countess of Wessex explained the Queen's choice in bold colours Photo: Getty Images

The Countess of Wessex, 51, explained why the monarch – her mother-in-law – famously opts for bold colors and big hats on public walkabouts. She said: "Don’t forget when she turns up somewhere, the crowds are two, three, four - ten, fifteen – deep. And somebody wants to be able to see that they saw a bit of the Queen’s hat as she went past. She needs to stand out - for people to be able to say ‘I saw the Queen.'"

In the two-hour documentary, which also featured contributions from the Prince of Wales, Duchess of Cornwalland Duke of Cambridge, Prince Harry revealed how continuing his grandmother’s work around the world can be daunting at times. He said: "People have always said, ‘do you feel as though you are following in her footsteps?’ That’s exactly what we are doing. There is nowhere on this planet that I can think of, that she hasn’t been in the last 90 years."

The Queen's birthday will be marked with many events Photo: Getty Images

"She has been everywhere and that’s sometimes quite hard, because you go to a place where she hasn’t visited for maybe 20 years, maybe 15, and you just think to yourself, ‘how can I ever fulfil this huge expectation that comes with her and being a member of her family?'"

Elsewhere the Queen’s cousin and close confidante Margaret Rhodes recalled playing a game called "catching happy days" with the young Princess Elizabeth and making up plays.

She said: "I can remember one occasion, I had to pick up and carry the Queen over the threshold… and of course I dropped her. She was very much an ordinary little girl, but she was always a slightly serious little girl as opposed to her younger sister who was always a very naughty little girl.

" In herself she is a very humble person, she has no huge opinion of herself, but has given up her life to that particular job that she was called to."

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